Active transmission line

ABSTRACT

An active transmission line simulating the operation of a nerve cell comprising a plurality of semiconductor elements each having the bulk negative resistance effect. Each element has a pair of mutually independent input and output terminals, one input terminal of one element being connected to one output terminal of the subsequent element. A signal applied to the center of the line is propagated in both directions and a signal applied at either end of the line is propagated toward the other end of the line.

United States Patent Hisayoshi Yanai Tokyo;

Fumio Hasegawa, Tokyo; Sugeta Takayuki, Tokyo; Nobuo Suzuki, Urawa, allof, Japan [72] Inventors References Cited OTHER REFERENCES Sugeta et aL,Proc. IEEE, Feb. 1968, pp. 239240, 307- 201 Primary ExaminerRoy LakeAssistant Examiner-Darwin R. Hostetter Attorney-Sandoe, Hopgood andCalimafde ABSTRACT: An active transmission line simulating the operationof a nerve cell comprising a plurality of semiconductor elements eachhaving the bulk negative resistance effect. Each element has a pair ofmutually independent input and output terminals, one input terminal ofone element being connected to one output terminal of the subsequentelement. A signal applied to the center of the line is propagated inboth directions and a signal applied at either end of the line ispropagated toward the other end of the line.

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INVENTORS HISAYOSHI YANAI 414/ d, ATTORNE 5 ACTIVE TRANSMISSION LINEThis invention relates to an active transmission line which is similarto the neural on and capable of nondistorted transmission.

BACKGROUND OF THE INVENTION The nerve fiber which transmits signals fromone nerve cell to another is an active line in which the signals are notattenuated and differs from the ordinary transmission line. The nervefiber has a static energy source and an active element in the form of aspatial distribution, in which the active element converts the staticenergy into a dynamic energy. This active line has an inherent pulsewaveform. Any waveform smaller than this inherent waveform is amplifiedduring transmission, and any larger waveform is attenuatedasymptotically to said inherent waveform. The nerve tissue may thus beconsidered as an ideal transmission line having a waveform-shapingfunctIon.

Several attempts have been made in the past to realize a transmissionline equivalent to the nerve fiber. For example, H. D. Crane proposedthe conception of the neuristor in Proceedings of the IRE," Oct. 1962,pages 2,048 to 2,060. Some neuristor lines have been realized to embodythis conception. For example, a transmission line associating Esakidiodes in a periodic arrangement has been proposed by I-Iayasaka andNishizawa in Joumal of institute of Electronics and CommunicationEngineers of Japan, Aug. 1966, pages 1,529 to 1,537. Also, Sugeta, lkomaand Yanai have jointly reported about a bulk neuristor element inProceeding of the IEEE, Feb. 1968, pages 239 to 240, which is formed byadding a plurality of input and output means to a semiconductingmaterial to bring about a propagating high field domain attributed tothe bulk negative resistance effect. In comparison with the neuristorusing an Esaki diode, the bulk neuristor element, utilizing thepropagating high field domain which is attributed to the bulk negativeresistance effect, is advantageous in view of the fact that the elementis structurally simple and its operating speed is high. A bulk neuristorelement utilizing a bulk negative resistance effect has been alreadyproposed by Sugeta et al. in the previously mentioned publication. Butin order to realize an active transmission line substantially similar tothe nerve fiber in its function by the use of the already-proposed bulkneuristor elements, the usage of many elements is required and thecircuit is very complicated.

It is, therefore, a principal object of this invention to provide anactive transmission line which is realized by a reduced number ofelements, is simple in circuit design, and is similar to the nerve fiberin its function, by associating semiconductors which possess the bulknegative resistance effect.

BRIEF SUMMARY OF THE INVENTION As described in the above-mentionedreports, the active transmission line is required to have: (1) the waveshaping function, (2) the threshold action, (3) a constantpulsepropagating velocity, (4) a nonresponding period or a refractoryperiod, and (5) bidirectionality. The requirements (1) through (4) canbe satisfied by utilizing the propagating high field domain which isattributed to the bulk negative resistance effect, as described inElectronic Material" of May 1967, pages 20 to 24. In the semiconductorelement utilizing the propagating high field domain, an output signalappears only when the input signal exceeds the threshold level. Theoutput signal is constant regardless of the value of the input signal.Moreover, the high field domain propagates from the cathode to the anodeat a definite high velocity, and the element is nonresponsive to theinput signal during the period when the propagating high field domainexists.

The transmission line of thisinvention comprises a plurality ofsemiconductor elements having said properties, each semiconductorelement having mutually independent input and output means. Thesemiconductor elements are connected organically to each other throughtheir input and output means, but the construction is not as complicatedas that of a transmission line composed of S and T junctions of bulkneuristor elements. As a result, this transmission line has the property(5) mentioned above. In the transmission line of this invention, asignal applied to the center of the line is propagated in bothdirections, a signal from the right is propagated to the left, and asignal from the left is propagated to the right. The propagated signalis not reflected at the end of the line, and two signals propagatedtoward each other collide and disappear.

To the accomplishment of the above and such other objects as mayhereinafter appear, the present invention relates to an activetransmission line as defined in the appended claims, and as described inthe following specification taken together with the accompanyingdrawing, in which:

FIG. 1 is a schematic diagram of a semiconductor active transmissionline in a preferred embodiment according to the invention; and

FIG. 2 is a voltage waveform diagram showing the operation of thetransmission line of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1, a plurality ofsemiconductor elements generally designated 11, 21, 31, 41 and 51 arecomposed of a suitable semiconductor material such as gallium arsenideor the like which has the bulk negative resistance effect. As typicallyshown by element 51, each element is provided with ohmic contacts (54and 54) at both ends respectively, only those contacts for element 51being shown in FIG. 1. The internal electric field of the semiconductormaterial is maintained above the sustaining field of the propagatinghigh field domain and below the threshold field by the use of a powersource E, connected across contacts 54 and 54'. The input terminal (forexample, 52, 52') of eachelement is mounted near the cathode electrode(for example, 54) thereof. Each element, therefore, responds to thepositive input pulse thereto, but does not respond to the negative inputpulse. Since the electric field between the cathode electrode (54) andinput terminal (52, 52) is strengthened by the positive input pulseapplied to the element, the high field domain may be formed. Theelectric field between the anode electrode (54) and the input terminal(52, 52) is, however, not sufficiently strengthened by the negativeinput pulse applied to the element to form a high field domain, becausethe distance between the input terminal and the anode electrode is fargreater than that between the input terminal and the cathode electrode.

Hereinafter, this invention will be explained in consideration that eachelement responds only to a positive input pulse.

Each of the semiconductor elements 11 through 51 is provided with pairsof signal input and output terminals 12, I2 and 13, 13; 52 and 52' and53 and 53' respectively. As shown in FIG. 1, an output terminal of oneelement is connected to an input terminal of another element, and aninput terminal of one element is connected to an output terminal ofanother element. The input terminal has a capacitive contact with theelement, so that the potential at an output terminal of one element isgiven as an input to the subsequent element in a differentiated form.

FIG. 2 illustrates the operation of the active transmission line shownin FIG. 1.

Assume that a pulse P is applied to the input terminal 12 ofsemiconductor element 11 at a time This pulse causes a propagating highfield domain to be formed in element 11, which high field domainpropagates from one end (left hand in FIG. I) to the other end (righthand in FIG. 1) of the element, so that the potential signal at outputterminals 13 and I3 is varied as shown by V as lapse of time. Thatpotential signal is differentiated through the capacitive couplingat theinput terminal of element 21 so that a=.positive pulse I, is applied tothat input tenninal at time t, and negative pulse is applied thereto attime when a high field domain passes through belowthe output terminals13 and 13' of the element 11.

Since the high field domain is formed in the element 21 only by thepositive pulse as mentioned above, a high field domain is formed in thesemiconductor element 21 at time 1,, i.e., when a positive pulse P comesin the element 11 but after the lapse of the time needed for thepropagating high field domain to be formed and for the signal to reachthe input terminal 22 from the output terminal 13'. Accordingly, thepotential at the output terminals 23 and 23' is also varied as indicatedby waveform V The potential at the output terminal 23 is delivered tothe input terminal 12 of the element 11 and to the input terminal 32 ofthe element 31 in the difierentiated form. At this time, since thepropagating high field domain, which has been formed in element 11 byinput pulse P is propagating in element 1 1, it is impossible for theinput pulse at input terminal 12' to form a high field domain in element11. At that time, there is no propagating high field domain insemiconductor element 31, and a propagating high field domain is formedin element 31 by the output pulse of element 21. As a result, thepotentials as the output terminals 33 and 33' are varied as shown by V,Consequently the output signal of element 31 is conveyed in thedifferentiated waveform to semiconductor element 41 in which a highfield domain does not yet exist. However, that signal is not conveyed toelement 21 because there has been already formed and now exists in thatelement a propagating high field domain. The elements 41, 51 operate ina similar manner as the elements 11 through 31. In this manner, theinput pulse applied to the input terminal 12 of this transmission lineis propagated from the semiconductor element 11 to element 51 by way ofelements 21, 31 and 41, and the pulse, after its waveform is shaped,comes out at the output terminal 53' at element 51. Similarly, when aninput pulse is applied to the input terminal 52', the signal ispropagated through the semiconductor elements 51, 41, 11, and deliveredto the output terminal 13 of element 1 1.

Now assume that two signals are simultaneously applied to thetransmission line; one signal from input terminal 12 on one end, and theother signal from input terminal 52' on the other end. The signalapplied to input terminal 12 is propagated through elements 11 and 21and sent to input terminal 32 of element 31. In the same manner, thesignal which entered the input terminal 52' reaches the input terminal32' of element 31. In element 31, only one high field domain is formedby both input signals at the input terminals 32 and 32'. Furthermore, ifboth input signals have a period therebetween, a high field domain isformed in element 31 by the first input signal so that it is not formedby the other input signal because a high field domain is alreadypropagating in the element at the time the other input signal is appliedto element 21. The output pulse of element 31 is propagated to the inputterminals of elements 21 and 42 in which a high field domain is stillpresent. Accordingly, high field domains cannot be formed in elements 21and 41 in which a high field domain is still present. Ac cordingly, highfield domains cannot be formed in elements 21 and 41 by the output pulseof element 31. Thus, the output pulse of element 31 cannot betransmitted to element 21 or to element 41, that is, the signalspropagated respectively from both ends of the transmission line collideat element 31 and disappear. Needless to say, the two signals woulddisappear even if these signals were applied at both ends of thetransmission line at slightly different times from each other.

Assume now that a signal is applied to element 31 which is in the middleof the transmission line. As in the foregoing case, the output ofelement 31 is propagated to the input terminals 22' and 42 of elements21 and 41 respectively. In this case,

there is no propagating high field domain in elements 21 and 41 so thatthe propagating high field domains can be formed by the input signalapplied thereto, and thus, output signals are produced by element 21 andelement 41. These output signals are then simultaneously propagatedrespectively in the direction of elements 11 and 51. in other words, thesignal applied to the middle of the transmission line is branched so asto be propagated in two directions after receiving waveform shaping,without being attenuated.

in the foregoing description, consideration 18 not given to the timeneeded for the signal to be propagated from the output terminal of onesemiconductor element to the input terminal of the subsequent element.However, it is necessary for the propagation of the signal that thelength of the semiconductor material be sufficiently long and thepropagating time of the high field domain be more than twice the timerequired for the signal to be propagated from the output terminal of oneelement to the input terminal of the subsequent element. In other words,it is necessary that the length of the propagating region of thepropagating high field domain in the element be longer than the productof the propagating speed of the high field domain and the time requiredfor the signal to go out from an element and to return to the sameelement by way of the input and output linkage defined by the input andoutput terminals interconnecting the various semiconductor elements. Ifthat is not so, the signal output from the one element (for example,output pulse P from the element 1 1) returns to the same element (forexample, input pulse P to the element 11), and generates the high fielddomain in that element. Namely, the signal remains in the one element.In the embodiment described, five semiconductor elements are used, butthe number of semiconductor elements is not confined to five; more thantwo elements may be used in correspondency to the length of the desiredtransmission line. Also, in the embodiment specifically shown, only acapacitive input terminal is employed for an input terminal, but anohmic terminal or a terminal based on a PN junction or a Schottkybarrier may be employed, provided that the output potential of one stageis differentiated by the coupling line or other suitable means and thenapplied as an input to the subsequent state.

It will thus be understood that variations to the specifically disclosedembodiment may be made without departing from the spirit and scope ofthe invention.

We claim:

1. An active transmission line comprising a plurality of semiconductorelements each of which has the capability of producing a propagatinghigh field domain attributable to the bulk negative resistance effect,each of said plurality of elements having mutually independent first andsecond input terminals and first and second output terminals, and meansfor coupling one of the input and output terminals of one of saidelements to one of the output and input terminals of another elementrespectively, to thereby establish an input and output linkage betweensaid semiconductor elements, said input terminals including means fordifferentiating the signal at the output terminal of the preceding oneof said elements, said coupling means including means for applying saiddifferentiated signal to the input terminal of the next one of saidelements, the length of the propagating region of the high field domainin each of said semiconductor elements being greater than the product ofthe propagating speed of the high field domain and the time required fora signal to go out from one of said elements and to return to said oneelement by way of said input and output linkage.

1. An active transmission line comprising a plurality of semiconductorelements each of which has the capability of producing a propagatinghigh field domain attributable to the bulk negative resistance effect,each of said plurality of elements having mutually independent first andsecond input terminals and first and second output terminals, and meansfor coupling one of the input and output terminals of one of saidelements to one of the output and input terminals of another elementrespectively, to thereby establish an input and output linkage betweensaid semiconductor elements, said input terminals including means fordifferentiating the signal at the output terminal of the preceding oneof said elements, said coupling means including means for applying saiddifferentiated signal to the input terminal of the next one of saidelements, the length of the propagating region of the high field domainin each of said semiconductor elements being greater than the product ofthe propagating speed of the high field domain and the time required fora signal to go out from one of said elements and to return to said oneelement by way of said input and output linkage.